Originally Posted by knightline
Hello All, This is my first ever post to the board...glad to be here!!!
I have a 1972 Chevy Monte Carlo with a 350 with intake and Holley 4bbl also I was told it has a mild RV cam in it. I bought the car like this. My problem is that after driving for about 3-5 miles I start to lose vacuum pressure it seems and my brake pedal gets real soft and low and hardly stops the car. Would this be a timing issue? I was told to add a vacuum storage tank, I havent done it yet but it seems I not getting enough vacuum so a tank would be useless. Please help a newbie out. Thanks in advance guys.
This sounds like a problem with the vacuum brake system, unless there as another source of a vacuum leak that comes on with some time related cause. An RV cam is not so wild as to affect vacuum to this point and if it did the vacuum would be low all of the time.
The first thing to do is get a vacuum gauge to monitor what's going on with the manifold vacuum. A large change several minutes into operation should be noticeable in how the engine operates. A loss of vacuum indicates that excess air is being drawn into the engine, if in fact this is happening, you would see it greatly upset the idle, it is not so apparent at higher RPMs because the throttle is more open so manifold vacuum is lower and leakage has less effect at that point of operation.